Hi samsue,
Sorry about the late response.
As I understand, you try to use object's material IDs to select a material's texture in a list of textures (Texmap)
Both Multi-Texture and Forest Color are designed for random generation, so won't work well in this case.
And Multi-Texture is not handling texmaps, just image filenames. (that's why it's UI is a bit special, allowing to drag and drop many textures from Windows explorer)
In fact, the name is misleading, it should be named 'Multi-Image' or 'Multi-Image Randomizer' instead.. sorry about that..
By updating the internal osl shader used for Forest Color, I could make a shader that should fit your purpose:
Plane01 has 6 material IDs from 1 to 6, and 2 'TexSelector10' osl textures, one for the diffuse, 1 for the bump
Plane003 has 10 materials IDs from 1 to 10, and a single TexSelector10 for the diffuse.
(Plane02, as a reference, uses the Material Selector)
Would this work for you ?
Is 10 slots enough ?
I could create a Wrapper for it, to avoid to set up the osl shader name and grayScale vertex attribute, and add a Reference Objects window as in the Multi-texture, to make sure objects have the Octane Geometry Modifier correctly setup.
Thanks